<template>
    <div class="pagination">
        <!-- <button :disabled="pageNo==1">上一页</button> -->
        <button v-show="pageNo > 1" @click="$emit('getPageNo',pageNo-1)">上一页</button>
        <button v-show="startNumAndEndNum.start > 1" @click="$emit('getPageNo',1)">1</button>
        <button v-show="startNumAndEndNum.start > 2">•••</button>

        <!-- 中间部分 -->
        <!-- 在外层套一层template放v-for遍历，防止v-for和v-if同时使用报错 -->
        <template v-for="(page,index) in startNumAndEndNum.end">
            <button 
            :key="index" 
            v-if="page>=startNumAndEndNum.start" 
            @click="$emit('getPageNo',page)"
            :class="{active:page == pageNo}"
            >
            {{ page }}
        </button>
        </template>

        <button v-show="startNumAndEndNum.end < totalPage-1">•••</button>
        <button v-show="startNumAndEndNum.end < totalPage" @click="$emit('getPageNo',totalPage)">{{ totalPage }}</button>
        <!-- <button :disabled="pageNo == totalPage">下一页</button>    -->
        <button v-show="pageNo < totalPage" @click="$emit('getPageNo',pageNo+1)">下一页</button>   
        <button style="margin-left: 30px">共 {{total}} 条</button>
    </div>
</template>

<script>
export default {
    name: "Pagination",
    // 父组件传递给的数据，当前页，每一页展示多少数据，数据总个数，连续页码数
    props:['pageNo','pageSize','total','continues'],
    computed:{
        // 总共多少页
        totalPage(){
            // 向上取整
            return Math.ceil(this.total/this.pageSize)
        },
        // 计算除连续的页码的起始数字和结束数字
        startNumAndEndNum(){
            // 解构赋值
            const {continues,pageNo,totalPage} = this
            let start = 0
            let end = 0
            // 连续的页码至少5,判断是否有5页
            if(continues > totalPage){
                // 总页码少于5
                start = 1
                end = totalPage
            }else{
                // 正常情况
                start = pageNo - parseInt(continues/2)
                end = pageNo + parseInt(continues/2)
                // 当start出现0和负数时进行判断
                if(start < 1){
                    start = 1
                    end = continues
                }
                // 当end大于最大页页码时进行判断
                if(end > totalPage){
                    start = totalPage - continues + 1
                    end = totalPage
                }
            }
            return{start,end}
        }
    },

}
</script>

<style lang="less" scoped>
.pagination {
    text-align: center;
    button {
        margin: 0 5px;
        background-color: #f4f4f5;
        color: #606266;
        outline: none;
        border-radius: 2px;
        padding: 0 4px;
        vertical-align: top;
        display: inline-block;
        font-size: 13px;
        min-width: 35.5px;
        height: 28px;
        line-height: 28px;
        cursor: pointer;
        box-sizing: border-box;
        text-align: center;
        border: 0;

        &[disabled] {
            color: #c0c4cc;
            cursor: not-allowed;
        }

        &.active {
            cursor: not-allowed;
            background-color: #409eff;
            color: #fff;
        }
    }
}
</style>
